W126 sudden heat loss - Page 3 - PeachParts Mercedes-Benz Forum

Gilly · #1 03-06-2013, 06:55 PM

Since the valve is capable of working, it would sort of point to the controller in the dash.
Interior temp sensor; maybe. Those seem to last the life of the car though, not much can go wrong with them.

LandYaghtLover · #2 03-06-2013, 08:01 PM

I re soldered my HVAC controls. No change. I did not have time to pull the plug on the mono valve since installing a new one. I need to try that.

I re-soldered the HVAC controls beacause a few days ago I had a hard fault on the controls. The air recirculation switch was steadily flashing and I had no control over the system. Not even able to turn it off. But get this, I had plenty of hot heat coming out.

Odd, huh? So thats why I need to try pulling the valve next.

But so far a new t-stat, new valve and re-soldering the controls has not helped. All vacuum lines look good. Idle is normal. I just need to keep tinkering when I have time, which is little.

MS Fowler · #3 03-06-2013, 08:37 PM

Just to say the obvious, ( somebody has to) Is the coolant level full?

LandYaghtLover · #4 03-06-2013, 08:54 PM

Yup. Burped, purged, etc. And its newer coolant. And even more new added when I replaced the t-stat in an attempt to resolve this. G-05 stuff.

Gilly · #5 03-06-2013, 09:14 PM

Remember the emergency default (ie NO power to the valve) is full heat.

LandYaghtLover · #6 03-06-2013, 09:16 PM

Right. So since it went default and I got tons of heat, be at low speed, I should have full heat with it unplugged. if I do, its one more part of the puzzle.

edit: before, I did not get any heat unplugged.

LandYaghtLover · #7 03-07-2013, 05:45 PM

Pretty sure the switch is part of the alarm system.

I have full egg-cooking heat though at low speeds. And when the system went into default on the highway I had full heat at low speed (when default, low speed fan is only option).

I am going to pull the plug on it tonight now that I am home early. I will see how the heat works over the next couple of days.

LandYaghtLover · #8 03-08-2013, 05:36 PM

Disconnected the new mono valve and have tons of uncontrollable heat. Figures. That rules out air pockets, etc.

hapsdoggen · #9 10-24-2013, 08:15 AM

Quote:

Originally Posted by LandYaghtLover

Disconnected the new mono valve and have tons of uncontrollable heat. Figures. That rules out air pockets, etc.

did you find the problem...?

i am having the same problems....

did you repair your monovalve with the MTC repair kit or did you buy and OEM monovalve...?

LandYaghtLover · #10 10-25-2013, 09:43 PM

I did not find the issue for certain yet. I did replace the parts with MTC. No change. So I took it apart again. This time I baked the solenoid on the over.

What I found is that the valve was leaking a bit. I think this flooded the solenoid. From what I can see, the solenoid was causing some electrolysis of the coolant by being exposed to it!!!

Anyway, after expensive cleaning and "drying out" I now have 100% heat at all times. Given that winter is here, I am okay with that for now. But when I have time I plan to remove the solenoid again and see how it moves when I adjust the temp. The plunger should move in and out. Voltage at the connector is fine and working with controls.

If I had a spare solenoid, I would just swap it out to test.

C Holmes · #11 11-03-2013, 07:13 AM

Does anyone here know if a monovalve from a w124 will work on the w126? They physically appear different but maybe an updated version as 124 is a 94 and 126 is a 90. I have a spare from the 124 and I think my 126 needs one.

sam196370 · #12 11-14-2013, 02:02 PM

I have a 91 560SEL and when I got it 6 years ago the monovalve was bad, replaced it and haven't had a problem until recently. Same issue, around town heat works GREAT, once on hwy it turns off. Just bought a genuine MB monovalve today from Pelican Parts, I've learned the hard way that when it comes to important stuff like heat or engine gaskets I always go genuine; cosmetic stuff I buy aftermarket - and am still disappointed by the low quality.

Sounds like your issue is still the MV.

C Holmes · #13 11-14-2013, 02:34 PM

Ya I am sure it is the M valve. I bought the "kit" from aftermarket and it will not fit in the electromagnet (waaay too tight) so I removed the circlips and swapped out the other parts. Put it in and had heat! till I got to highway

Anyway now not sure what to do with it. Need heat I live in Nova Scotia. Not sure why it wont work now tho, It really should I think.